1. Field of the Invention
The present invention relates to a hearing aid. More specifically, the present invention relates to a hearing aid which is provided with a semiconductor memory cell including a field effect transistor having the function of converting a change in an amount of charges or polarization to an amount of currents, and to a hearing aid capable of adjusting its characteristics in accordance with a user and a usage environment.
2. Description of the Related Art
FIG. 26 shows the configuration of a conventional hearing aid having a digital signal processing function. This hearing aid 50 includes a central processing unit (CPU) 56, a data memory 57, a digital processing circuit 53, an A/D converter 52, a D/A converter 54, an amplification circuit 55, an output circuit 58, a microphone 51 and a loudspeaker 59. When a sound is inputted to the hearing aid 50 from the microphone 51, a sound signal outputted from the microphone 51 is amplified by the amplification circuit 55, converted from the analog signal to a digital signal by the A/D converter 52, processed by the digital processing circuit 53 to be suited to user's characteristics, converted from the digital signal to an analog signal by the D/A converter 54, and outputted to the loudspeaker 59 through the output circuit 58. Further, on the basis of a series of parameters that determine hearing aid characteristics stored in the data memory 57, the CPU 56 controls the digital processing circuit 53. In the above-described hearing aid 50, the digital processing circuit 53 converts an output level relative to an input level for each frequency band.
Following the recent improvement of the performance of the hearing aid, the hearing aid can be adjusted to a user's usage environment. Accordingly, there have been proposed an adjustment method of adjusting the hearing aid by connecting the hearing aid to a personal computer and transferring adjustment data from the personal computer to the hearing aid.
In FIG. 26, components that are required to connect the hearing aid 50 to an external adjustment apparatus (e.g., a personal computer) following the adjustment are not shown. For example, a terminal extending from the personal computer is connected to a battery contact, whereby the personal computer is connected to the CPU 56 shown in FIG. 26.
At the time of adjusting such a hearing aid, the personal computer creates the adjustment data for adjusting the characteristics of the hearing aid to be suited to the user's characteristics and transfers the adjustment data to the hearing aid 50. The adjustment data transferred to the hearing aid 50 is stored in the data memory 57. The CPU 56 controls the digital processing circuit 53 on the basis of the adjustment data stored in this data memory 57. The digital processing circuit 53 processes the sound signal so as to be suited to the user's characteristics. The hearing aid user can, therefore, listen to the sound suited to his or her characteristics.
The data memory 57 includes a rewritable semiconductor memory cell. Normally, as the rewritable semiconductor memory cell, an electrically erasable programmable ROM (EEPROM) is employed in many cases. Literatures that disclose related techniques are, for example, as follows: Japanese Patent No. 2638563, and Japanese Unexamined Patent Publication No. 2001-148899.
However, if the hearing aid includes the above-described digital processing circuit and the like, the size of the hearing aid is made large and, also, the cost thereof increases. Among the components of the hearing aid, the cost of the data memory 57 particularly occupies most of the overall cost of the hearing aid 50. Therefore, the cost hike of this data memory 57 poses a significant problem.